In the absence of forced convection, an electronic apparatus will be hotter at the top of its external enclosure than at the bottom. The situation is worse for apparatus sealed for use outside where internally generated heat has to be dissipated by the external enclosure. Ideally components which generate large amounts of heat would be sited lower in the external enclosure than components which generate less heat. However, that is not always possible.
Heat pipes have been used to conduct heat away from components to cooler positions in the external enclosure. Conventionally, the evaporator of a heat pipe is in direct thermal contact with a power component e.g. by clamping or bonding. The condenser of the heat pipe is conventionally pressed into a groove in the wall of the external enclosure, being an interference fit in the groove so as to ensure good thermal contact. The heat pipe has a round cross section and the groove has a corresponding round bottom. The step of pressing the heat pipe into the groove may also be used to distort the pipe so that it finishes flush with the top of the groove.
A problem with this is that removal of the heat pipe is virtually impossible which makes removal of the circuit board on which the component is mounted very difficult.
In some external enclosures individual units have to be isolated from one another against radio frequency (RF) interference by closed internal housings. Another problem with using the heat pipe as described above is that it would be difficult to maintain the RF isolation around a heat pipe that would have to enter the internal housing.